1. Field of the Invention
This invention relates to a circuit switching system which switches a circuit to a facsimile after a telephone receives a call incoming via the circuit.
2. Description of the Prior Art
Conventionally, a structure shown in FIG. 1 is used to allow a telephone and a facsimile to use in common a circuit connected to a PBX (Private Branch Exchange) and/or a button telephone. When circuits 3.sub.1, 3.sub.2 and 3.sub.3 are connected to PBX 1, a circuit changing switch 4 is provided in the circuit 3.sub.3 to allow same to be connected to either one of PBX 1 and a facsimile 5, the switch 4 is arranged to normally connect PBX 1 and circuit 3.sub.3. If this system is called up using a telephone number allocated to the circuit 3.sub.3 in order to transmit an original document to facsimile 5, any one of telephones 2.sub.1 -2.sub.n will be called up via PBX 1. When a responder answers this call by a predetermined one of telephones 2.sub.1 -2.sub.n, he will be required to switch the switch 4 to the facsimile. After manual switching, facsimile communication is performed via circuit 3.sub.3.
This system allows the telephone and facsimile to use the circuit 3.sub.3 in common, but switching the switch 4 is troublesome and inconvenient.
In an attempt to cope with these problems, a circuit shown in FIG. 2 is proposed in which a special telephone 6 is connected to PBX 1 in addition to telephones 2.sub.1 -2.sub.n. A switch 8, which is switched by a signal on a signal line 7.sub.1 extending from the telephone 6, is disposed between PBX 1 and circuit 3.sub.3 with facsimile 5 being connected to switch 8. Switch 8 is controlled so as to normally connect the circuit 3.sub.3 and PBX 1. The facsimile 5 is controlled, started and stopped via a signal line 7.sub.2 extending from telephone 6. In this system, a call incoming via circuit 3.sub.3 is transmitted via PBX 1 to the telephone 6. If the call is responded by telephone 6, transmission of an original document to facsimile 5 is requested. When a predetermined operation is performed by pressing buttons at telephone 6, a control signal is delivered to the signal lines 7.sub.1 and 7.sub.2, the switch 8 is switched so as to connect the circuit 3.sub.3 and facsimile 5 and to start facsimile 5. The document transmission side starts facsimile transmission via the circuit 3.sub.3 after switching has been finished.
Handling this system is not troublesome because the switch 8 is not required to be changed manually. However, the special telephone 6 is required to control switch 8 and facsimile 5. In addition, there is a call incoming at the circuit 3.sub.3, it is delivered to the telephone 6, so that when the telephone 6 is used by another circuit (for example, 3.sub.1 or 3.sub.2), it is impossible to transmit an original document to facsimile 5. In order to avoid this inconvenience, all the telephones 2.sub.1 -2.sub.n could have the same structure as the telephone 6. However, the use of more than a few special telephones would increase the entire cost and the number of signal lines and complicate the structure of the system.
As described above, the use of a switch such as the circuit changing switch 4 shown in FIG. 1 renders manual changing troublesome. The use of a system such as that shown in FIG. 2 not only requires special telephones, but also makes it impossible to transmit information to a facsimile if the special telephone is in use. In order to cope with this inconvenient situation, all the system telephones could be replaced with special telephones such as those mentioned above. However, this would increase the cost of the system and complicate the system due to an increase in the number of control signal lines. This invention derives from the consideration of drawbacks in such conventional circuit switching system.
The object of this invention is to provide a circuit switching system which eliminates troublesome manual switching and allows a telephone and a facsimile to use a circuit in common without relying upon a special telephone.